Doctors reported that many people are asking for flu vaccine in the mistaken belief that if they develop flu-like symptoms after they have been vaccinated, they will know they have anthrax. The early symptoms of anthrax resemble the flu.

"We want to separate the idea that getting vaccinated [for flu] increases or decreases your fears about getting anthrax," said Keiji Fukuda, an epidemiologist at the Centers for Disease Control and Prevention. "When people get vaccinated against influenza they have decreased their chances of getting the flu, but they can get infected by cold viruses."

Influenza causes far more deaths -- about 20,000 a year in the United States -- than does anthrax. Some public health experts said the flu's toll ought to prompt nearly everyone to be vaccinated, which would require more vaccine than is now available. Manufacturers have sent about 45 million doses of flu vaccine to clinics and hospitals this fall, and 40 million more are scheduled to be shipped soon.